Marshall, Keynes, and Macroeconomics

Marshall's notion of the representative firm can be read as a macro
notion with some resemblance to Keynes' aggregative concepts.
Keynes' notions of aggregate demand and aggregate supply are
fashioned after Marshall's definitions of demand and supply. Keynes
starts with the Marshallian equilibrium notion. The main innovation
of Keynes--a conception of macroeconomic analysis as distinct from
microeconomic analysis--may be understood as a particular
application of Marshall's moving equilibrium method.